The Claim: Caffeine Causes Dehydration

Medical experts have been saying for years that caffeine acts as a potent diuretic. Consume too many caffeinated beverages, and you end up drinking yourself into dehydration.

But research has not confirmed that notion. Most studies have found that in moderate amounts, caffeine has only mild diuretic effects — much like water.

Photo

Credit
Leif Parsons

One report, by a scientist at the University of Connecticut who reviewed 10 previous studies, appeared in June 2002 in The International Journal of Sport Nutrition and Exercise Metabolism.

Investigations comparing caffeine with water or placebo seldom found a statistical difference in urine volume, the author wrote. “In the 10 studies reviewed, consumption of a caffeinated beverage resulted in 0 to 84 percent retention of the initial volume ingested, whereas consumption of water resulted in 0 to 81 percent retention.”

Another study, in the same journal in 2005, involved scientists following 59 active adults over 11 days while controlling their caffeine intake. They were given caffeine in capsule form on some days and on other days were given a placebo. Researchers found no significant differences in levels of excreted electrolytes or urine volume.